.TH std::chrono::round(std::chrono::duration) 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::chrono::round(std::chrono::duration) \- std::chrono::round(std::chrono::duration)

.SH Synopsis
   Defined in header <chrono>
   template< class ToDuration, class Rep, class Period >
   constexpr ToDuration round( const std::chrono::duration<Rep, Period>&  \fI(since C++17)\fP
   d );

   Returns the value t representable in ToDuration that is the closest to d. If there
   are two such values, returns the even value (that is, the value t such that t % 2 ==
   0).

   The function does not participate in the overload resolution unless ToDuration is a
   specialization of std::chrono::duration and
   std::chrono::treat_as_floating_point_v<typename ToDuration::rep> is false.

.SH Parameters

   d - duration to convert

.SH Return value

   d rounded to the nearest duration of type ToDuration, rounding to even in halfway
   cases.

.SH Possible implementation

   namespace detail
   {
       template<class> inline constexpr bool is_duration_v = false;
       template<class Rep, class Period> inline constexpr bool is_duration_v<
           std::chrono::duration<Rep, Period>> = true;
   }

   template<class To, class Rep, class Period,
            class = std::enable_if_t<detail::is_duration_v<To> &&
                   !std::chrono::treat_as_floating_point_v<typename To::rep>>>
   constexpr To round(const std::chrono::duration<Rep, Period>& d)
   {
       To t0 = std::chrono::floor<To>(d);
       To t1 = t0 + To{1};
       auto diff0 = d - t0;
       auto diff1 = t1 - d;
       if (diff0 == diff1)
       {
           if (t0.count() & 1)
               return t1;
           return t0;
       }
       else if (diff0 < diff1)
           return t0;
       return t1;
   }

.SH Example


// Run this code

 #include <chrono>
 #include <iomanip>
 #include <iostream>

 int main()
 {
     using namespace std::chrono_literals;
     std::cout << "Duration\\tFloor\\tRound\\tCeil\\n";
     for (using Sec = std::chrono::seconds;
         auto const d : {+4999ms, +5000ms, +5001ms, +5499ms, +5500ms, +5999ms,
                         -4999ms, -5000ms, -5001ms, -5499ms, -5500ms, -5999ms})
         std::cout << std::showpos << d << "\\t\\t"
                   << std::chrono::floor<Sec>(d) << '\\t'
                   << std::chrono::round<Sec>(d) << '\\t'
                   << std::chrono::ceil <Sec>(d) << '\\n';
 }

.SH Output:

 Duration        Floor   Round   Ceil
 +4999ms         +4s     +5s     +5s
 +5000ms         +5s     +5s     +5s
 +5001ms         +5s     +5s     +6s
 +5499ms         +5s     +5s     +6s
 +5500ms         +5s     +6s     +6s
 +5999ms         +5s     +6s     +6s
 -4999ms         -5s     -5s     -4s
 -5000ms         -5s     -5s     -5s
 -5001ms         -6s     -5s     -5s
 -5499ms         -6s     -5s     -5s
 -5500ms         -6s     -6s     -5s
 -5999ms         -6s     -6s     -5s

.SH See also

   duration_cast                  converts a duration to another, with a different tick
   \fI(C++11)\fP                        interval
                                  \fI(function template)\fP
   floor(std::chrono::duration)   converts a duration to another, rounding down
   \fI(C++17)\fP                        \fI(function template)\fP
   ceil(std::chrono::duration)    converts a duration to another, rounding up
   \fI(C++17)\fP                        \fI(function template)\fP
   round(std::chrono::time_point) converts a time_point to another, rounding to
   \fI(C++17)\fP                        nearest, ties to even
                                  \fI(function template)\fP
   round
   roundf
   roundl
   lround
   lroundf
   lroundl
   llround
   llroundf                       nearest integer, rounding away from zero in halfway
   llroundl                       cases
   \fI(C++11)\fP                        \fI(function)\fP
   \fI(C++11)\fP
   \fI(C++11)\fP
   \fI(C++11)\fP
   \fI(C++11)\fP
   \fI(C++11)\fP
   \fI(C++11)\fP
   \fI(C++11)\fP
   \fI(C++11)\fP
